Electrically operated loads of this nature may be provided in large numbers in complex automated control systems such as, for example, a sewing-machine plant. Since a malfunction of a single operating circuit may affect large parts of the system, these circuits require frequent checking to ascertain possible irregularities.
Conventionally, such checking is done with the aid of voltmeters or ammeters to be connected across or inserted in a circuit suspected of being defective. The integrity or the defective condition of a circuit may be indicated visually or acoustically by means of lamps, buzzers or the like.
These conventional testing methods are relatively cumbersome and must be carried out by skilled personnel. They generally require a disconnection of the circuit element to be checked from the associated driver whose own performance, therefore, cannot be tested by such a procedure.